Understanding the specifics of an old home before renovating
Identifying the original materials and walls: stone, brick, wattle-and-daub, timber framing
Before any renovation, identify what the walls and floors are actually made of. A stone, brick, wattle-and-daub, or timber-framed house doesn't respond to water and heat the same way. The idea is simple: understanding the wall means not blocking its exchanges and creating condensation. A local survey, a record of the renders and joints, and a few photos of open areas save time.
Spotting common issues: moisture, saltpeter, cracks, insufficient ventilation
The symptoms speak for themselves. Moisture traces, odors, saltpeter, blackening wood, growing cracks, and rooms that feel "stuffy." Treat the causes first: infiltration, rising damp, ventilation defects. Otherwise, even high-performance insulation can turn into a trap.
Defining your priorities: winter comfort, summer comfort, energy savings, heritage preservation
Set your goals. Winter comfort, summer comfort, the bill, or respecting the building. Then prioritize: dry out and ventilate, then insulate, then choose the heating system. Dry out and ventilate, then insulate, then choose the heating system. An energy audit helps make these trade-offs without altering the character of the house.
Making the right diagnosis for a coherent renovation (audit and on-site surveys)
An energy audit, supplemented with on-site surveys, avoids renovating blind. You cross-reference usage, bills, and plans, then check on site. The goal: spot the losses and build a coherent work scenario.
Essential on-site surveys: thicknesses, thermal bridges, windows, attics, floors
On site, note insulation thicknesses, wall-floor and wall-roof junctions, shutter boxes and window reveals. Record the windows (glazing type, condition of the seals), the condition of the attic and ground floors. Photos and sketches. Simple measurements, safer decisions.
Moisture and ventilation: measure, understand, treat before insulating
Before insulating, measure relative humidity, look for condensation, infiltration, and rising damp. Check the existing ventilation (air inlets, vents, mechanical ventilation, flow rates) and any parasitic air leaks. Without fresh air, insulation can trap water. Treat this first.
Choosing the order of work: avoiding "patches" and aiming for a high-performance renovation
The most robust order follows the energy logic. First, airtightness and insulation. Then suitable ventilation. Finally, heating and hot water sized to the reduced needs. This avoids the "patch" of replacing the heat generator too early. High-performance renovation.
Insulating without damage: solutions suited to historic buildings and heritage
Wall insulation: external or internal, depending on the facade, heritage constraints, and use
In historic buildings, external insulation is often the most effective, but it can be limited by a protected facade, moldings, or a ruling from the ABF (France's Architects of Buildings of France). In that case, internal insulation remains possible if you treat the thermal bridges and choose vapor-permeable insulation materials so the walls can still manage moisture. Also think about service runs and window sills. This is where the renovation is won or lost, down to the millimeter.
Attic and roof insulation: airtightness, vapor barrier, specific points
Attics are a rich source of savings, provided you take care of airtightness before piling on insulation. Vapor barrier or vapor retarder depending on the wall, continuity around hatches, ducts, and pipes. And if the roof breathes, check the ventilation and the roof underlays to avoid condensation.
Ground floors and cellars: limiting losses without trapping moisture
Under the floor, favor insulation from below when accessible, keeping a ventilated cellar or crawl space. Avoid solutions that trap water in the masonry. Treat the edges, openings, and thresholds, then check for rising damp. The goal: comfort without mold.
Heating, hot water, and ventilation: the winning trio after insulation
After successful insulation, the next step comes down to getting the order of adjustments right. In renovation, you secure comfort, lower the bill, and avoid moisture-related issues.
Right-sizing right after the work: avoiding oversizing and short cycling
A better-insulated house needs less power. Have the heat losses recalculated after the work, then adjust the emitters and controls. An oversized unit cycles on and off repeatedly and wears out faster. The goal: useful power and stable operation.
Heat pump, boiler, stove: choosing based on the building, use, and existing network
High-temperature radiators, underfloor heating, existing gas, wood storage, everything counts. An air-to-water heat pump works very well on a suitable distribution network. A boiler can still make sense if gas is available and the need is high. A stove complements a system, with a good distribution network.
Suitable ventilation: mechanical ventilation, air inlets, controlled renewal to protect the building
The more you insulate, the more the air needs to be controlled. Check the air inlets, the balancing, and the extraction. Humidity-sensing single-flow mechanical ventilation or heat-recovery ventilation depending on budget and airtightness. Healthy air protects the building and limits mold.
2026 aid schemes and rules to know to secure your renovation job sites
MaPrimeRénov' and CEE in 2026: points to watch, documents to prepare, mistakes that block files
For MaPrimeRénov', secure the file before signing the quote when the rule requires it. Prepare identity documents, tax notice, proof of ownership, DPE or audit depending on the pathway, bank details, and dated, complete quotes. For CEE, keep the targeted standardized sheet, the signed sworn statement, and invoices with performance figures, surfaces, and product references. Classic blockers come from a non-compliant quote, an inconsistent date, or wording that doesn't match the requirements. To go further on the causes of rejection, see how to avoid MaPrimeRénov' file rejections.
RGE certification and installation requirements: traceability, technical data sheets, possible checks
In renovation, the RGE certification needs to cover the right area, at the right time. Keep photo proof, technical data sheets, batch numbers, installation diagrams, and adjustment or commissioning instructions. Checks can target compliance with the quote, the declared performance, and installation quality. A well-organized file saves time.
Special heritage cases: facade, ABF, local rules, and how to plan ahead for delays
In a heritage area, external insulation or a change in appearance can trigger a review by the ABF, a prior declaration, or a permit. Plan ahead for the requirements (colors, materials, moldings) and the review timelines. The right instinct is to sort out the planning application before it holds up the job-site schedule.
Key figures
R = 0.3 to 0.5
Stone walls
50 to 70%
Indoor relative humidity
Frequently asked questions
Favor vapor-permeable systems (NHL/CL lime render, lime-hemp, lime or silicate paints) and avoid sealed films like cement or oil-based paint. On historic buildings, the rule is to preserve the wall's ability to release water vapor: an adhesion test and a survey of the existing render before reworking it avoid incompatibilities.
Pierre-Louis Guhur
CEO of Argile
